It is only shallow people who do not judge by appearances. –Oscar Wilde, Picture of Dorian Gray

Forensic scientists begin their testimony even before they speak their first words. Even before they take the oath or recite their qualifications, the jury is assessing their credibility by their demeanor. Simply put, demeanor evidence is the body’s compass, pointing in the direction of credibility. It includes gestures, intonations, posture, mannerisms, eye movements, inflections, and expressions. Judges and juries listen and look very closely to demeanor evidence to assess the credibility of forensic testimony. Research has repeatedly shown that demeanor evidence significantly determines court decisions.¹ Recently the U.S. Supreme Court has reinforced the importance of demeanor evidence in the 2009 case of Melendez-Diaz v. Massachusetts.²

That decision required forensic scientists to personally testify to their research and conclusions. The Melendez-Diaz Court based its decision on the 6th Amendment’s Confrontation Clause and stressed the essential practice of jurors to see and to hear people testify, not just examine affidavits. Forensic Magazine has tracked the progress and discussed the significance of the Melendez-Diaz case for forensic scientists.³ Before Melendez-Diaz, it was common practice for forensic scientists to submit their results by affidavits. This will no longer be the standard practice. Forensic science testimony now requires as much attention to the manner in which they testify as to their scientific research. It is no longer enough to be good scientists, forensic experts need to be effective communicators.

Because it is unlikely they will have had testimony training or education in their formal schooling, forensic scientists will need to get additional training, particularly in communication and persuasion skills, human relations, and relaxation techniques.

Demeanor Evidence and Forensic Scientists
While research shows that demeanor evidence immediately and significantly impacts the jury’s evaluations of credibility, it is the “Cinderella” of forensic science. Its significance is often overlooked and ignored. Demeanor is left holding the mop and broom when her sisters go off to the ball to thrill in the dance of DNA and digital evidence. Melendez-Diaz has helped reinvigorate the significance of demeanor evidence. That case’s majority opinion made clear that the Confrontation Clause intended to help judges and juries to distinguish between accurate, clear, and forthright testimony and testimony that misses that standard.⁴ At the same time, neuroscience and behavior scientists continue to show the importance of witness demeanor for legal decisions. Demeanor is the Prince Charming that can sweep both Cinderella and the jury off their feet.

This analogy might be hard to believe. After all, isn’t law about cold, hard facts? Don’t juries want to hear the cool, linear logic of hard scientific research from forensic scientists when considering the evidence? The answer is that judges and jurors rely on demeanor evidence every bit as much as in hearing facts and in logically considering them.⁵ Legal researchers, social scientists, and neuroscientists are studying how courts and juries use demeanor evidence to assess credibility. Because jurors have used demeanor evidence from the beginning of our judicial system and Melendez-Diaz now often requires personal testimony, forensic scientists will need training to comport their personal demeanor to their scientific deliberations.